Torsional vibration dampers are employed extensively in internal combustion engines to reduce torsional vibrations delivered to rotatable shafts. The torsional vibrations may be of considerable amplitude, and, if not abated, can potentially damage gears or similar structures attached to the rotatable shaft and cause fatigue failure of the rotatable shaft.
Torsional vibration dampers convert the kinetic vibrational energy by dissipating it to thermal energy as a result of damping. The absorption of the vibrational energy lowers the strength requirements of the rotatable shaft and thereby lowers the required weight of the shaft. The torsional vibration damper also has a direct effect on inhibiting vibration of nearby components of the internal combustion engine that would be affected by the vibration.
The simplest insertion style torsional vibration damper has three components, a hub that allows the damper to be rigidly connected to the source of the vibration, an inertia ring, and an elastomeric strip in the same shape as the ring. The elastomeric strip provides the spring dashpot system for the damper. Typically, the hub and the inertia ring are manufactured individually and machined before the elastomer is inserted by force into the gap that is present between the hub and the inertia ring. The elastomer is compressed and exerts a pressure between the metallic surfaces of the ring and hub, holding the assembly together. There are several design problems with these dampers.
The hub of the crankshaft damper can be formed in a variety of different matters, and, in particular, can be cast. Various casting methods can be used. Shell casting utilizes two mold halves that are combined together and filled with molten metal. This casting method will inherently leave a parting line where the two mold halves join. Further, this molding technique causes the formation of a casting gate, which is an imperfection or boss located where the metal is poured into the mold. In the past, such cast hubs had to be machined prior to assembly.